Consumer Reports found that of the 16 products that included caffeine levels on labels, five overshot the listed amount by more than 20%. Another sample had 70% less caffeine than was advertised on the container.

Many energy drinks were showcased in stores near the soda and juice sections and occasionally at the checkout aisles, but rarely near alcohol, according to the study.

The test results came as federal health officials probe recent reports that, since 2009, five people have died from consuming Monster Beverage Corp.’s energy drinks. The Corona company said it is “unaware of any fatality anywhere that has been caused by its drinks.”

The Consumer Reports study and Monster investigation were cited in a letter from two U.S. senators asking the Food and Drug Administration to address regulatory loopholes and possible health risks related to energy drinks.

On Friday, Sens. Richard J. Durbin (D-Ill.) and Richard Blumenthal (D-Conn.) sent the letter – their third – calling on the agency to look into the industry and its effect on children and teens. The lawmakers also requested more scrutiny of ingredients such as guarana, taurine and ginseng, which are often used in energy drinks.

The letter also sought better guidelines on energy drink classifications, claiming that companies often categorize the products as dietary supplements to skirt regulatory oversight but then market the items as beverages.

Even as caffeine-pumped products such as the AeroShot Energy inhaler spark health concerns, energy drink sales are booming. Last year, they soared nearly 17%, according to industry publication Beverage Digest.

In 2010, Four Loko took caffeine, guarana and taurine out of its alcoholic beverages, reformulating the products "after trying - unsuccessfully - to navigate a difficult and politically-charged regulatory environment at both the state and federal levels," said maker Phusion Projects in a statement.

You might be surprised by the biggest beer brands worldwide. Sure, Budweiser and Heinken have spots on the list, as expected. But there’s also a selection of international beers just now becoming popular in the U.S. And just try to guess the top beer label as ranked by trade publication the Drinks...